1. Field of the Invention
The present invention relates to a cleaning nozzle applicable to a wide range of cleaning operations on automobiles, buildings' wall surfaces, bottles and dishes, and more specifically to an improved cleaning nozzle that has an improved performance of mixing and accelerating a gas and a cleaning liquid to enhance a uniformity of the gas-liquid mixture flow containing droplets of the cleaning liquid and to eject the liquid droplets at high speed. This invention also relates to an improved technique to prevent a passage clogging due to a powder material which can occur when the powder material is used to take advantage of its delaminating action in further improving the performance of removing sticky dirt.
The present application is based on Japanese Patent Applications No. 2000-199749, 2000-199750 and 2000-363890, which are incorporated herein by reference.
2. Description of the Related Art
The cleaning nozzle of this kind for ejecting a gas-liquid mixture flow is known to be available in two types: one in which a gas ejection port is provided on the outside, enclosing a liquid ejection port, and one in which a liquid ejection port is provided on the outside, enclosing a gas ejection port. The present invention relates to an improvement in the former type in which the gas ejection port is provided on the outside. In the cleaning nozzle that utilizes the cleaning action of the gas-liquid mixture flow, the state and ejection speed of the gas-liquid mixture flow ejected from the cleaning nozzle are important. That is, the higher the ejection speed of the liquid droplets, the greater the physical action produced by the liquid droplets striking against the target surface being cleansed and the better the resultant cleaning action. If the gas-liquid mixture state is good and the liquid droplets are highly uniform, a stable cleaning action can be obtained. For example, a technical means is disclosed (Unexamined Japanese Patent Publication Sho. 60-261566 and Unexamined Japanese Patent Publication Hei. 10-156229) in which a trumpet-shaped portion is formed upstream of a minimum diameter portion of the nozzle and in which the cross-sectional area of the gas passage in the trumpet-shaped portion is progressively throttled to accelerate the gas as it is mixed with the liquid.
With the conventional technique, however, because the passage cross section is simply throttled at the trumpet-shaped portion formed upstream of the minimum diameter portion of the nozzle, there is a limit to the mixing of gas and liquid and the acceleration of droplets. Hence, there is a room for improvement.
As for the aforementioned conventional techniques, more detailed explanations are provided hereinafter.
In Unexamined Japanese Patent Publication Sho. 60-261566, there is disclosed such that a gas ejection portion in the nozzle is formed as a converging-diverging tube, which is once narrowed and progressively expands toward the downstream end thereafter, in order to accelerate the gas to a sonic or supersonic speed before mixing it with a liquid. This conventional technology has the following drawbacks. Because a ring-shaped ejection port, which is installed in the narrow gas ejection portion in the nozzle, must have a narrow converging-diverging shape in a longitudinal cross section, not only does the structure of the gas ejection portion become complex and difficult to machine but also the nozzle cannot always eject a high-speed gas-liquid mixture flow. In the case of a nozzle made of a straight cylindrical tube, it is technically impossible to increase the ejection speed above the sonic speed even by coordinating or improving the ejection conditions. In other words, the structure of the straight tube ejection nozzle imposes a limitation on an increase in the ejection speed.
Further, in a Laval nozzle or converging-diverging nozzle which has a trumpet-shaped portion in front of a minimum diameter portion and a diverging tapered portion after the minimum diameter portion, if a relative pressure relationship among the trumpet-shaped inlet portion, the minimum diameter portion and the tapered outlet portion is adjusted properly, the flow speed at the rear tapered portion increases to a sonic speed or even supersonic speed—a speed increasing phenomenon widely known in the fluidics (see “Mechanical Engineering Handbook” published by Japan Mechanical Engineers Association (Nihon Kikai Gakkai) (Apr. 15, 1987), A5-page 58). Under these circumstances, a technique for increasing ejection speed has been proposed which uses a converging-diverging nozzle or Laval nozzle to realize a supersonic ejection speed in Unexamined Japanese Patent Publication Hei. 10-156229. Although this conventional technique discloses, as a means of realizing a supersonic flow speed, an abstract method of increasing the ejection speed to a supersonic speed by utilizing the speed increasing phenomenon at the rear tapered portion of the Laval nozzle, it fails to give a sufficient explanation on the state of the gas-liquid mixture flow ejected from the nozzle, i.e., as to how a uniformly distributed liquid droplets can be ejected stably.
Furthermore, in a cleaning nozzle which mixes gas and liquid therein to form and eject a gas-liquid mixture flow as the cleaning medium, when a powder material is added to take advantage of the delaminating action of the powder, a problem arises that the powder accumulates in parts of the passage where the flow speed slows down or where flow resistance is large, degrading the performance of the cleaning nozzle. When the powder used is water-soluble powder, such as sodium hydrogencarbonate, the powder easily absorbs humidity and turns into a solid lump that adheres to the wall surface of the passage. Further, the powder easily adheres to and cloggs on protrusions and stepped portions in a passage of the cleaning nozzle. When using hard powder, the passage may be damaged.